The microstructural characteristics of cast Mg-x Sn (x = 0.5, 1.0, 2.5 wt.% and 4.0 wt.%) alloys were systematically evaluated, as well as the electrochemical behavior and discharge properties in 3.5 wt.% NaCl solution. The micro-morphological results show that the grains are obviously refined and the Mg₂Sn phase distribution is uniform with the increase of Sn content. In the four tested alloys, the effect of Sn content on the corrosion resistance of the alloys was found to be bidirectional by using the loss-in-weight method and electrochemical measurements. Among them, Mg-2.5Sn exhibits higher corrosion resistance in 3.5 wt.% NaCl solution. The decrease of the self-corrosion rate of Mg-x Sn alloy is mainly due to the formation of a SnO₂ protective film, which inhibits the expansion of pitting corrosion. In addition, an appropriate amount of Mg₂Sn can weaken the self-corrosion behavior. Mg-1Sn exhibits the highest anode efficiency and discharge capacity of 56.11% and 1245.72 mAh·g⁻¹, respectively. Mg-0.5Sn shows the highest peak energy density, which is 1258.78 mWh·g⁻¹.The maximum average discharge voltage of Mg-2.5Sn is 1.461 V.